Remember that the easiest way to open the intercom without the key is to call someone close and ask them to open the door. You can also call the neighbor and explain the situation. Problems with access to the entrance should arise.
If no one is home or you are about to enter into someone else's door, for example, to visit friends, and the floor, feel free to call through the intercom in any, in the entrance (usually above the door sign range of apartments, which can be accessed via the entrance) and ask them to open the door. All the neighbors usually know each other. Explain to whom you are going to pass and you will open. You can also go to the trick and say, for example, that rented an apartment in the building, and forgot the keys to the intercom. Ask them to open the door. If you're convincing, then you will also open.
Remember that the door is equipped with intercom, you can open, using physical force. Lock that is opened via intercom, magnetic. Despite the fact that the magnets in the lock quite strongly attracted to each other, if you put a lot of effort, they can be separated. So if you are very much pulled at the door handle, it opens. In order to exert the greatest force, one foot rest against the wall of the house, grasp with both hands the handle of the door and tug sharply. If at first you don't succeed, try again. Be careful and mind your head in that moment, when the door opens. Despite the fact that the castle in this opening is not damaged, the method is "barbaric", so to resort to it only in extreme cases.
Remember that with many entrances sit Granny or young people who can learn the entry code to get to the entrance. Peacefully and politely explain why you need to open the door. Do not be rude or be rude and you will get positive feedback.